The floating drum biogas plant is the most popular type of low-cost biogas plants in India. These plants use feedstock from households and small farming activity. Organic matter as raw manure enters the digester and comes out as quality fertilizer after a retention of typically 40 – 60 days in the digester. Out comes also biogas consisting of about 60 % methane. This simple construction is most suitable in warm tropical or subtropical climates.
The biogas plant has no stirring, heating system or any advanced monitoring system. The digester has a floating steel drum on top of the slurry. The drum rises and sinks according to if gas is produced or consumed. It could be made from locally available materials as cement and plastic bags.
In addition to being inexpensive and simple, this plant is also robust, easy to operate and require little maintenance.
A 4-stroke Otto engine could be used. This engine can relatively simply be modified to be run on biogas and still being able to use gasoline as a back-up solution if the compression ratio is not increased too severely. In contrast to pilot-injection engine (diesel engine alternative) the otto engine can be driven on 100 % biogas. The engine could be mechanically connected to a pump in a portable pump-set.
As a way to transport the gas, balloon storage is a very good alternative. To keep the system as simple and low-cost as possible, the gas flow during consumption could be controlled by placing weights on top of the balloon. A plate could be used to couple the weights.